Suggested Citation:
Sohnen, Julia (2013) Electric Vehicle Charging and the California Power Sector: Evaluating the Effect of Location and Time on Greenhouse Gas Emissions. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-13-21

This thesis explores the implications of the increased adoption of plug-in electric vehicles in California through its effect on the operation of the state’s electric grid. The well-to-­wheels emissions associated with driving an electric vehicle depend on the resource mix of the electricity grid used to charge the battery. We present a new least-­cost dispatch model, EDGE-NET, for the California electricity grid consisting of interconnected sub-­regions that encompass the six largest state utilities that can be used to evaluate the impact of growing electric vehicle demand on existing power grid infrastructure system and energy resources. This model considers spatiality and temporal dynamics of energy demand and supply when determining the regional impacts of additional charging profiles on the current electricity network.

Model simulation runs for one year show generation and transmission congestion to be reasonable similar to historical data. Model simulation results show that average emissions and system costs associated with electricity generation vary significantly by time of day, season, and location. Marginal cost and emissions also exhibit seasonal and diurnal differences, but show less spatial variation. Sensitivity of demand analysis shows that the relative changes to average emissions and system costs respond asymmetrically to increases and decreases in electricity demand. These results depend on grid mix at the time and the marginal power plant type.

In minimizing total system cost, the model will choose to dispatch the lowestâ€cost resource to meet additional vehicle demand, regardless of location, as long as transmission capacity is available. Location of electric vehicle charging has a small effect on the marginal greenhouse gas emissions associated with additional generation, due to electricity losses in the transmission grid. We use a geographically explicit, charging assessment model for California to develop and compare the effects of two charging profiles. Comparison of these two basic scenarios points to savings in greenhouse gas emissions savings and operational costs from delayed charging of electric vehicles. Vehicle charging simulations confirm that plug-­in electric vehicles alone are unlikely to require additional generation or transmission infrastructure.

EDGE-­NET was successfully bench marked against historical data for the present grid but additional work is required to expand the model for future scenario evaluation. We discuss how the model might be adapted for high penetrations of variable renewable energy resources, and the use of grid storage. Renewable resources such as wind and solar vary in California vary significantly by timeâ€of-­day, season, and location. However, combination of multiple resources from different geographic regions through transmission grid interconnection is expected to help mitigate the impacts of variability. EDGEâ€NET can evaluate interaction of supply and demand through the existing transmission infrastructure and can identify any critical network bottlenecks or areas for expansion. For this reason, EDGE-­NET will be an important tool to evaluate energy policy scenarios.